Since Cubase (Elements, Artist and Pro) 9.0.10, the layout of affected windows can be reset as follows:

Select 'Windows...' from the 'Window' menu.

A dialog window opens showing a list of currently opened windows.

Select the affected window in the list.

Click on 'Reset Layout'.

If you reset the layout of the MixConsole, the MixConsole window will be closed. Next time you open it, the standard layout will be restored.

If you reset the layout of the Project window, you will be asked to save the project and to restart Cubase. It is recommendable to create a backup of the project by saving the project under a new name. Next time you start Cubase the standard layout will be restored.